This invention relates to a resin composition having excellent heat-resistance and workability, and more in detail to a heat-resistant thermosetting resin composition obtained by reaction with each other of an N,N'-bis-imide of unsaturated dicarboxylic acid (A), a cyanuric or isocyanuric acid or derivatives thereof (B), and at least one compound (C) selected from the group consisting of tetracarboxylic acid diimide, hydantoin and derivatives thereof, and barbituric acid and derivatives thereof.
As the heat-resistant polyimide resin a polyimide resin of Du Pont type is well known which is obtained by condensation polymerization, and immediately following dehydration reaction, of diamine with a tetracarboxylic acid anhydride typically represented by pyromellitic anhydride. This polyimide resin is excellent in heat-resistance but its resinous solution (prior to the dehydration reaction) is low in stability. Further, since this polyimide resin presents the difficulties in terms of workability as attributed to the occurrence of dehydration reaction, the volatilization of low molecular compounds, etc. in the course of its resinification, it is not suitable to the fabrication of a molding and laminated sheet.
A polyimide resin of Rhone-Poulenc type is also known which is obtained by reacting diamine with an N,N'-bis-maleimide (see, for example, U.S. Pat. No. 3,562,223). This type of polyimide resin is not followed by a dehydration reaction in the course of its solidification and therefore is suitable to the manufacture of a laminated sheet, but is insufficient in mechanical strength such as bending strength. Where aliphatic polyamine is used as diamine, the reaction proceeds rapidly but the resulting polyimide resin is low in heat-resistance. Where aromatic polyamine is used as diamine, the reaction time covers several to scores of hours at a temperature of, for example, 160.degree. to 250.degree. C even in the case of a fusing method.
A method of producing a polyimide resin from reaction of N,N'-bis-imide with isocyanuric acid is also attempted (see, for example, U.S. Pat. No. 3,770,705). In this method, however, not only the reaction process is complicated but also is the resulting polyimide resin insufficient in terms of electric properties.